The International Hydrographic Organization (IHO) has published a number of publications that standardize how ENC data should be encoded, visualized and protected:

  • S-57 (IHO Transfer Standard for Digital Hydrographic Data) is the standard used for the exchange of digital hydrographic data between national hydrographic offices and for its distribution to manufacturers, mariners and other data users. It defines how ENC cell data should be physically encoded to files.

    The S-57 implementation is based upon the IHO Transfer Standard for Digital Hydrographic Data - Special Publication No. 57 - Edition 3.1 - November 2000.

  • S-52 (Specifications for Chart Content and Display Aspects of ECDIS) specifies how ENCs should be visualized on a map. It provides a symbology set and a number of rules that rigorously define how each individual object in an ENC cell should be displayed, by specifying the symbol, color and line style.

    The S-52 implementation is based upon the Specifications for Chart Content and Display Aspects of ECDIS - Special Publication No. 52, and the IHO Presentation Library User’s Manual - Edition 3.4 - January 2008.

  • S-63 (IHO Data Protection Scheme) provides a mechanism to encrypt and protect ENC data from unauthorized use.

These publications can be downloaded from the IHO website at the following location:

Parts of the S-52 specification are not freely available, but need to be purchased via the IHO office.

Although S-57 was initially designed for the encoding of ENC data, the standard can also be used for the encoding of other products. One such product is Additional Military Layers (AML), which is used for the encoding of military nautical data. Another is InlandECDIS (IENC), used for river navigation.

The IENC feature and attribute resources, as well as the visualization rules, are based on the InlandECDIS specification version 2.4. You can use it to open IENC versions 2.0, 2.1, 2.2, 2.3 and 2.4.

The AML feature and attribute resources are based upon the AML Feature and Attribute Catalogue version 3.0.1.

The visualization of AML is based on the AML Portrayal Specification version 3.0.0.

Reference information on AML, including the Feature and Attribute Catalogue, can be downloaded at the following location: